Conn. Gen. Stat. § 12-704k: Credit for residents who challenge taxes imposed on certain income by another jurisdiction.

For taxable years commencing on or after January 1, 2020:

(1) A resident of this state who satisfies the provisions of subparagraphs (A) to (D), inclusive, of this subdivision shall be allowed a credit against the tax otherwise due for the applicable taxable year under this chapter, other than the liability imposed by section 12-707, in an amount equal to sixty per cent of the amount of taxes owed to this state as a result of the readjustment of the credit for taxes paid to another state of the United States or a political subdivision thereof or the District of Columbia, pursuant to section 12-704. To be eligible for the credit under this section, such resident shall have:

(A) Paid any income tax or wage tax imposed for the taxable year by another state of the United States or a political subdivision thereof or the District of Columbia;

(B) Applied for and been denied a refund from such other jurisdiction for taxes paid to such other jurisdiction on income derived from services rendered while such resident was within this state;

(C) Filed an appeal with a court or tribunal through which such resident formally protested such denial; and

(D) Obtained a final decision that resulted in such other jurisdiction refunding to such resident taxes paid to such other jurisdiction on income derived from services rendered while such resident was within this state.

(2) No penalty or interest shall be imposed on any late payment of the tax due under this chapter, other than the liability imposed by section 12-707, if (A) such late payment is attributable to a reduction in the credit for taxes paid under section 12-704, (B) such reduction in the credit for taxes paid is the direct result of a refund that a resident of this state received from another state of the United States or a political subdivision thereof or the District of Columbia, (C) such refund relates to income derived from services rendered while such resident was not within such other jurisdiction, and (D) such other jurisdiction requires employee income to be sourced to an employer's location if a nonresident renders services from an out-of-state location.